CHING-HUI WU, TSU-JEN LIN, and TSU-MU KAO

Abstract:

The results of the internal fire events analysis in a Level 1, power operation probabilistic safety assessment (PSA) for a pressurized water reactor (PWR) plant in Taiwan was updated in the late 1990's. This fire analysis adopted a scenario-based PSA approach to systematically evaluate the fire and smoke hazards and their associated risk impacts on the PWR plant. The analysis was divided into two phases: spatial interaction analysis phase (also known as the screening phase) and detailed analysis phase. In the screening phase, it was determined that the contributions to core damage frequency (CDF) from such fire risk-insignificant zones as administration building, radwaste building, etc. were relatively low. The remaining fire zones were further evaluated quantitatively to identify the risk-significant zones using a risk criterion of "greater than 0.1 percent of the internal events CDF". The main control room and the identified risk-significant zones were analyzed in detail in the second phase. The analysis of the main control room adopted a more refined methodology based on a panel-oriented scenario analysis. The extensive fire growth modelling was performed using the COMPBRN-IIIe code for the risk important fire zones. The plant model used in this analysis, which was developed and quantified using the WinNUPRA software to estimate the CCDP, was based on the living PSA models of the PWR plant completed in December 1995. The plant models were modified to reflect the impact of fire scenarios on human events and recovery actions. EXCEL® spreadsheets were used for the evaluation and integration of the fire risks. For the detailed analysis of fire sub-scenarios, the CDF of a fire sub-scenario was derived by multiplying the fire initiating event frequency, the conditional core damage probability, and the fire hazard factors associated with the sub-scenario. Five fire hazard factors were used to account for some of the effects of fire and smoke in the fire PSA model. This paper presents the results of the fire PSA updates and discusses the risk impacts associated with the fire hazard factors. These fire analysis results are the bases for the advanced risk-informed fire analyses performed for the cable tray wrapping at the PWR plant in Taiwan.